Optical Line Terminal Research Articles

Flexible coherent UDWDM-PON with dynamic user allocation based on limited-tunability lasers

Coherent wavelength division multiplexing (WDM) technologies have leveraged the optical communication systems in core networks, increasing the fiber capacity by transmission with advanced modulation formats and mitigation of impairments with digital signal processing. However, these solutions are too expensive for access networks, where cost, power budget, and footprint are limited. Hence, the key technology will be developing low-cost coherent transceivers providing an excellent selectivity and giving high sensitivity, which allows high splitting ratios. This paper reports an experimental design of a low-cost coherent ultra-dense WDM passive optical network (UDWDM-PON) with 6.25 GHz channel spacing. The users’ optical network unit (ONU) is built employing coherent transceivers with two paired low-cost distributed feedback (DFB) lasers, one as the local oscillator and another as the transmitter, offering simplicity and low-cost hardware; likewise, the optical line terminal (OLT) at the central office can profit from the same design. The ONU DFB lasers have wavelengths with limited thermal tunability, controlled by a thermo-electric cooler, which is used to allocate the wavelengths. A medium access control (MAC) at the OLT manages the spectrum channel allocation for ONUs, demanding connection when activation is requested: the OLT furnishes an optical carrier wavelength for the ONU to obtain connection by a control algorithm, assigning a down-channel and another paired up-channel assigned to the ONU DFB transmitter. The MAC can reassign the channels because of interference or collision in a dynamic wavelength allocation. Measures in an activation process and in channel reassignment have been performed in environmental conditions, including control signals and the physical parameters of DFB lasers, demonstrating the practical viability of the PON scaling from 32 up to 256 wavelength channels.

Automated provisioning method for a modular PON-OLT device toward Plug & Provision

We propose a new automation concept for access network equipment called “Plug & Provision.” This concept aims at reducing the workload in provisioning passive optical network (PON) service by utilizing a modular optical line terminal (OLT) and automating the setup sequence. To realize this concept, the automation platform must automatically detect the modular OLT plugged into a switch port and execute the configuration sequence that it triggered. We utilize open-source software in the control/management layer, especially focusing on OpenFlow as a control protocol. We present the overall architecture including a newly proposed PON abstraction and in-band control method for deeply disaggregated modular OLTs, and we demonstrate the feasibility of the architecture.

Development of Testing Standardization Regulation of the OLT XG-PON Equipments to Support Broadband Access in Indonesia

This study aims to provide a reference to the technical specifications of the Optical Line Termination (OLT) XG-PON equipment for improving standardization regulations (Perdirjen Postel No. 257 of 2008). The technical specifications tested in this study are the nominal rate capability, wavelength range, and jumbo frame of the OLT XG-PON equipment. The research acquired a reference to the nominal rate using FEC is 8.5 Gbps downstream direction, and 2.5 Gbps upstream direction, upstream wavelength range is 1260-1280 nm and downstream is 1575-1581 nm, and jumbo frame capability is 2000 Bytes.

Global load-balancing ONU assignment for a software-defined reconfigurable PON

Rapidly growing and fluctuating traffic demands lead to unbalanced traffic scenarios in optical access networks, which have an impact on network efficiency. Thus, the flexible software-defined reconfigurable passive optical network (PON) architecture has been proposed to handle this challenge. To improve the efficiency of a reconfigurable PON facing unbalanced traffic demands, this paper proposes a global load-balancing (GLB) optical network unit (ONU) assignment method, which aims to achieve load balancing among the optical line terminals (OLTs) in the OLT pool as well as among the aggregation switch ports that connect the OLTs by optimizing the affiliations between the OLTs and the ONUs. For on-line optimization, a greedy GLB algorithm is introduced that regroups the ONUs and generates load-balanced target ONU-OLT affiliations in accordance with dynamic traffic demands. For off-line optimization, bee colony optimization (BCO) is invoked to search for better ONU regrouping solutions for GLB. Simulation results show that the proposed GLB algorithm can significantly improve the throughput and delay performance of an optical access network faced with unbalanced traffic demands, especially when the network load is heavy. Moreover, the proposed BCO technique for GLB can obviously improve the worst delay performance and reduce the migrated traffic of the GLB solution, especially under network conditions with high peer-to-peer traffic proportions and heavy network loads. Thus, the proposed global load-balancing ONU assignment method is effective for helping a software-defined reconfigurable PON to cope with unbalanced traffic demands.

Mini-PON: disaggregated module-type PON architecture for realizing various PON deployments

We propose a new optical access network concept named “Mini-PON.” This concept features the separation of passive optical network (PON)-optical line terminal (OLT) functions into micro module-type hardware that offers switch port pluggability and minimal modular software running on a server to literally minimize the space needed for PON deployment, giving more flexibility to operators who want to deploy PONs in various fields quickly and cost effectively. We explore the optimal function split between hardware and software to balance performance and flexibility. A prototype demonstrates that the proposed implementation architecture can perform as well as a conventional PON in terms of throughput and upstream latency, while also realizing (i) dynamic bandwidth allocation softwarization and modularization via standards-based application programming interfaces and (ii) remote placement of the hardware module from the central office on which the OLT software runs: both are key advances.

Research on Power Optimization Based on Adaptive Passive Optical Networks

Abstract For the commercial wavelength division multiplexing passive optical network (WDM-PON) with standard single-mode fiber SSMF-28 and 1:64 passive fiber branching at its far end (RN) and 100 GHz C-band continuous wavelength (CW) lasers, the maximum coverage and optimal transmission power of STM-16 and STM-64 with external modulators at different speeds and wave numbers (4λ, 8λ and 16λ) are obtained, respectively. The performance parameter of the high data rate WDM-PON system is analyzed with respect to a number of channels and reach. In order to improve the network utilization and receiving efficiency, the influence of different channels and transmission distances on the performance of high data rate WDM-PON system is analyzed. Simulation analysis with Optisystem15.0. The maximum transmission power required to achieve the maximum transmission distance under the condition of nonlinear constraints is obtained. In order to save power consumption, the configuration of each multi-band PON is optimized in terms of transmission power. It is found that WDM-PON system has to compromise between aggregated data rate and system reach. Future software defined access network reconfigure the access network depending on the dynamic demand and the resources available. Hence depending on the distance between the optical line terminal (OLT) and optical network unit (ONU) guaranteed data rate can be estimated. ONU is equipped with a tunable optical filter (TOF) hence future wavelength can be reconfigured by both service provider and user. It makes it possible for software to customize optical access network.

A mode transformation algorithm based on traffic prediction in virtual multi‐OLT PON

SummaryIn this paper, a mode transformation algorithm based on traffic prediction in virtual multiple optical line terminal (OLT) passive optical network (PON) is proposed. By proposing exponential smoothing algorithm based on weight update (WU‐ESA), user traffic is predicted well. WU‐ESA is a combination of two algorithms: exponential smoothing algorithm (ESA) and genetic algorithm (GA). The weight in ESA is optimized by GA based on real‐number encoding. By setting two periods, GA part and ESA part can be separated effectively. By presenting elastic packing algorithm (EPA), the load balance problem in virtual multi‐OLT PON is solved. EPA is implemented based on WU‐ESA. By the simulation and analysis, the effectiveness of the proposed algorithms is demonstrated. Compared with traditional mode transformation algorithm, EPA shows good performances in delay, throughput, and packet loss. Compared with traditional mode transformation algorithm, the EPA makes the packet loss decrease by at least 5% when the system load is greater than 0.9. Meanwhile, the delay of the two subsystems can be kept at a relatively balanced level by the implement of EPA. For throughput, the use of EPA improves the throughput by 20% when the system load is high.

Implementation of network-coding approach for improving the BER performance in non-orthogonal multiple access (NOMA)-PON

In the current passive optical networks (PONs), we address the challenge of dealing with asymmetric channel conditions and asymmetric data rates in order to meet the traffic demand of optical network unit (ONU) to ONU (O2O) communications. A joint network-coding (NC) and power domain non-orthogonal multiple access (NOMA) approach (NC-NOMA) is discussed. The novelty of this NC-NOMA scheme lies in the way the inter-ONUs communicates with an optical line terminal (OLT) at different modulation formats. Specifically, in the uplink communications, at each ONU side, multiple data streams from different ONUs are superimposed into one single symbol. Meanwhile, NOMA is considered by adjusting the optical transmission power of ONUs such that the OLT can decode the signals from different ONUs based on successive interference cancellation (SIC). At the OLT side, the adding zeros approach at the specific positions of the shorter bit sequence is introduced. In the downlink communications, the ONUs obtain their own data by decoding the received messages. By applying NC-NOMA, the ONU with better channel condition only needs to demodulate the fictitious symbols with a low order modulation format instead of demodulating the symbols with a high order modulation format. The simulation results show NC-NOMA with hierarchical adding zeros approach outperforms NC-NOMA with traditional zero padding approach in terms of having lower average end-to-end BER of ONUs without having additional complexity.

Resource Allocation and QoS Guarantees for Real World IP Traffic in Integrated XG-PON and IEEE802.11e EDCA Networks

Globally, there is a significant rise in the number of connected devices. Every device has an access to wide variety of telecom services among which voice, video and best effort (BE) contribute significantly. There is a noticeable growing trend towards upstream BE traffic besides real time e-services that demand high quality of service (QoS). Converged next-generation fiber-wireless (FiWi) access networks composed of next-generation passive optical network (XG-PON) and 802.11n based wireless local area network (WLAN) has emerged as a suitable choice to provide high quality and affordable e-services to plenty of subscribers as they possess both high bandwidth and flexibility. In this paper, we study the performance of the integrated network architecture which combines XG-PON and enhanced distributed channel access (EDCA) under real time bursty traffic derived from the current global IP traffic distribution. The joint tuning of various crucial parameters of both XG-PON and EDCA with incorporation of an efficient deficit dynamic bandwidth algorithm (DBA) at optical line terminal (OLT) is done by exhaustive simulations in network simulator-3 (NS-3). Through intensive simulations and tuning, we are able to achieve a end-to-end delay performance of <; 150 ms for voice, <; 500 ms for video and a few seconds for BE upto full capacity. Also, a packet loss ratio (PLR) of <; 3% and <; 6% is achieved for voice and BE respectively upto full load. For voice PLR is <; 1% upto 60% total offered load. Further, it is observed that the fine tuning of key parameters has also resulted in increased bandwidth for dominant BE services. Therefore, this optimized network architecture is 20% more fair to BE services as compared to the conventional integrated FiWi architectures.

Enhancement of Spectral Efficiency and Power Budget in WDN-PON Employing LDPC-Coded Probabilistic Shaping PAM8

A $5\times60$ Gb/s low-density parity-check (LDPC) coded WDM-PON using 8-level pulse amplitude modulation (PAM8) signals with probabilistic shaping (PS) over 20-km standard single-mode fiber (SSMF) with direct detection is proposed and experimentally demonstrated. Each optical carrier at the optical line terminal (OLT) carries a 20-Gbaud probabilistically-shaped LDPC-coded PS-PAM8 signal from a conventional uniform PAM16 signal following a designed approximate Gaussian distribution (AGD). A LDPC-based bit-interleaved coded modulation scheme with iterative decoding (BICM-ID) is utilized to recover the inherently overlapped symbols due to the proposed PS mapping. Combining decision-directed least-mean-squares (DD-LMS) and constant modulus algorithm (CMA), a blind feedback pre-equalizer is adopted to reduce the frequency loss of the signal owing to imperfect electro-optical components in experiment. As for experimental verification and application, 1.48-dB superior receiver power sensitivity and 1.7-dB launch fiber power optimization are gained respectively by using LDPC-coded PS-PAM8 signals in WDM-PON, which can bring higher spectral efficiency and power loss budget for the optical distribution networks.

A Framework for an Energy-Efficient Bandwidth Allocation Approach through Dynamic ONTs Grouping in Flexible GPON Access Networks

The growing demands for high speed connectivity to keep pace with bandwidth intensive applications and services have spawned the idea of developing PONs with capabilities beyond those of copper and wireless-based technologies in access network. In this article, an approach for the design of an energy efficient bandwidth allocation mechanism for the shared upstream communication link in the Fiber to the Home (FTTH) access network is presented and evaluated using Mixed Integer Linear Programming (MILP) model. In the MILP model, two objective functions for minimization of power consumption and minimization of blocking were evaluated. The results have shown that with the objective of power minimization approach, Optical Network Terminals (ONTs) are efficiently grouped to the minimum number of active networking Optical Line Terminal (OLT) switches, traffic is groomed, ports are efficiently utilized, and hence total power consumption is minimized. Results have shown that with energy efficient bandwidth allocation approach consideration, energy savings can reach up to 80% for different examined traffic loads following uniform distribution.

Two dimensional optimized enhanced multi diagonal code for OCDMA passive optical networks

This paper optimizes the design of two-dimensional enhanced multi diagonal (2D-EMD) code and conventional spectral/spatial (SS) optical code division multiple access system architecture for large capacity at relatively low powers. The existing 2D-EMD coding scheme is optimized by reducing the weight and length of spatial code sequence to minimize power losses across the encoding and decoding arrangement. Moreover, a complete system architecture is developed by optimizing the structures of conventional 2D SS optical line terminal (OLT) and remote node (RN) racks to reduce the use to long span optical fibers between the central office and subscribers premises. The optimized system architecture is implemented as per passive optical network (PON) specification in Optisystem and analysis is performed using several pivotal performance parameters. It is observed that optimization of the 2D-EMD (2D-OEMD) coding algorithm elevates both transmission capacity and cardinality at received powers as low as of − 10 dBm. Moreover, the new OLT and RN racks significantly reduces the length and number of optical fibers between the OLT and receiver modules. Consequently, the optimized SS 2D-OEMD system can support 192 subscribers at 2 Gbps of data each over the span of 25 km single mode fiber. Consequently, the proposed architecture can be adapted for numerous application with high bandwidth requirement including next generation PON, back bone for free space optical and fifth generation communication systems.

Experiment Study of Downstream Traffic Balancing Strategy on 40G Long Reach Coherent PON

Abstract Distributed high-bandwidth consumption services such as cloud computing require large-capacity, long-distance, and wide-coverage development requirements for Next-Generation Passive Optical Networks (NG-PON2). With the development of NG-PON2 technology, the optical line terminal (OLT) device structure of passive optical network (PON) system is also increasingly complex and heterogeneous. This leads to the problem of network congestion and low bandwidth utilization caused by the unbalanced use of link and port resources in the traditional core network in the PON network. Based on the 40G coherent PON experimental system, this paper studies the traffic balancing problem of OLT equipment, and proposes a dynamic traffic balancing strategy based on real-time monitoring of load sharing and reporting of police and periodic adjustment. The experimental results show that the designed dynamic traffic balancing strategy can effectively reduce the PON network blocking rate and improve bandwidth utilization.

Improved self-seeding and carrier remodulation performance for WDM-PON by means of double RSOA erasure

In this work, we investigated a novel wavelength division multiplexing passive optical network (WDM-PON) configuration, based on cascaded reflective semiconductor optical amplifiers (RSOA) data erasure for combined self-seeding and wavelength reuse. Improved performance is achieved by enhanced erasure efficiency using a self-seeded double-RSOA cavity at the optical line terminal (OLT) and cascaded RSOAs at the optical network terminal (ONT). To carry out the study, our experimental results for our earlier combined topology layout operating at a symmetric transmission were used to validate the simulation framework for the proposed double-RSOA erasure configuration. Using our original single-cavity self-seeding WDM-PON architecture as a benchmark, downstream extinction ratio (ERD) margins of 6.5 dB and 9.0 dB are obtained, for generating self-seeded downstream signals and upstream remodulation, respectively. Also, bidirectional transmission of 1.25 Gb/s over links reach up to 45 km is achieved by the double-RSOA cavity, surpassing in 25 km our original combined topology. The results indicated that our proposition effectively addresses a fundamental trade-off for WDM-PONs based on the wavelength reuse and/or self-seeding techniques. Specifically, the double erasure procedure allows the use of relatively high levels of ERD, thereby providing improved bit error rate (BER) at the ONT, while assuring high-quality generation of the self-seeding carrier and loopback operation.

Strategies to increase spectral efficiency and energy saving with quality metric assurance in TWDM-PON

We propose a methodology for planning TWDM-PON that combines three lines of approach, known from literature, into a single approach that establishes a trade-off among them. That may support the network designer in finding a solution that can, simultaneously, meet high bandwidth demands, keep assurance of quality of service (QoS) level agreed with users, and increase energy saving of the network by taking into account the users’ activity and bandwidth sharing in the network. To develop the proposed algorithm, two bandwidth management techniques have been analyzed aiming at a possible migration of the end user equipment (optical network unit, ONU), whereas possible, in a more efficient distribution of ONU per wavelength pair (downstream-upstream). As a result, it becomes possible to switch off some management interfaces, thus assuring a degree of energy save. In parallel, two methods for providing an adaptive record of ONUs were aggregated to improve the performance of those ONUs that are migrating and/or entering the network, thus avoiding collision between signals and increasing the chance of their registration in the optical line terminal (OLT). The paper also addresses the fulfillment of the service level agreement (SLA), signed by operators and users, and proposes ways for designing a TWDM-PON that offers services with a quality metric assurance. Different scenarios with variable percentage of active users were considered and it was noticed that, in more realistic scenarios (50%, in average, of active ONUs), the network saved almost 50% of energy at the interfaces to be configured, with a migration period around 5 min. Additionally, it reached a SLA close to 100%, which is above the usual when it comes to compliance services. In addition, to meet bandwidth demand up to 1 Gb/s, the QoS was evaluated in four common Split Ratios (1:8 to 1:64) that the TWDM-PON can be configured, from the simplest to the most complex scenarios (active user, p, from 10% to 100%). In this way, it was verified that for the network to comply with satisfactory QoS, minimum percentage of time during which the target bit rate should be available for each connected user, the TWDM-PON should be planned at different activity levels, and the best planning are (p = 100%, 1:8), (p = 70%, 1:16), (p = 40%, 1:32) and (p = 20%, 1:64).

Hierarchical modulation PAM4 with digital Nyquist pulse-shaped for flexible multi-ONU provisioning in NG-TDM PON

Abstract In this paper, we study the performance of digital Nyquist-shaped and hierarchical modulation four-level pulse amplitude modulation (N-HM-PAM4), which is one of the most cost-effective modulations, in the context of the intensity-modulation and direct-detection (IM/DD) enabled the next generation time division multiplexed passive optical network (NG-TDM PON). In addition, by considering the power fading (which is incurred by the chromatic dispersion (CD)) and linear and nonlinear inter-symbol interference (ISI) (which is incurred by CD and square-law photo-detection) during the transmission, vestigial side band (VSB) optical equalization, overlap frequency-domain equalization (OFDE), and iterative nonlinear ISI digital domain compensation are applied in the system to improve both bandwidth efficiency and receiver sensitivity. Simulation results show how different parameters of the N-HM-PAM4 based NG-TDM PON (i.e., optical modulation index (OMI), iterative cancellation number, power ratio, and the distance between the optical line terminal (OLT) and its optical network units (ONUs)) affect the performance of the system, which is defined as the bit error ratio (BER) and received optical power (ROP) of the ONU.

Heuristic polling sequence to enhance sleep count of EPON

Next-generation passive optical networks (PONs) demand power conservation to create a green environment. A reduction in power consumption of the traditional Ethernet passive optical network (EPON) can be achieved by increasing the sleep count in optical network units (ONUs). In this paper, this is accomplished by introducing a first-in-last-out (FILO) polling sequence in the place of a fixed polling sequence to increase the number of ONUs entering sleep mode (sleep count). In a fixed polling sequence, the optical line terminal (OLT) allocates idle time to the ONUs based on the overall load of the ONUs. This leads to a situation that whenever the idle time does not meet the wakeup time threshold of sleep mode, the ONUs are put into doze/active mode, which consumes more power. In the FILO polling sequence, the first polled ONU in the current cycle is made to be polled last in the following cycle. Polling continues in this way, and by this rearrangement, the idle time of delayed poll ONUs increases; hence, it helps to reduce the power consumption. Additionally, a modified load adaptive sequence arrangement (MLASA) method is suggested, where the ONUs are categorized into doze ONUs and sleep ONUs. A numerical simulation of the FILO polling sequence with a vertical cavity surface emitting laser (VCSEL) ONU shows a maximum reduction in power consumption of 15.5 Wand a 20% improvement in energy savings compared with the traditional fixed polling sequence. The MLASA method results in better power consumption with minimum delay than that of the proposed FILO and existing LASA methods.

Wavelength and Bandwidth Allocation for Mobile Fronthaul in TWDM-PON

Time- and wavelength- division multiplexed passive optical network (TWDM-PON) has attracted considerable attention for the next generation optical access systems. Among potential applications of TWDM-PON, a major application is the support of mobile fronthaul streams between radio units (RUs) and distributed units (DUs) in the centralized radio access network (C-RAN) architecture, which consists of central units (CUs), DUs, and RUs. The upstream fronthaul traffic that an optical line terminal (OLT) receives is expected to become highly bursty due to the variable data rate generated by employing new functional split options and the synchronization of data transmission between neighboring RUs caused by time-division duplex (TDD). However, there has been no wavelength and bandwidth allocation scheme for TWDM-PON that is designed to efficiently accommodate fronthaul streams satisfying the strict delay requirement. Therefore, in this paper we propose a novel wavelength and bandwidth allocation algorithm that can minimize the number of active wavelength channels considering the high burstiness and delay requirement of fronthaul data transmission. Through computer simulations it was confirmed that the number of active wavelength channels can be reduced by 50% with the proposed algorithm, and thus more RUs can be efficiently accommodated using TWDM-PON.

A Novel Scheme for UDWDM-PON Broadband Access Network Using Injection-Locked Phase-to-Intensity Modulation Converter

Abstract In this paper, we have proposed and analyzed a novel cost-effective ultradense wavelength division multiplexed (UDWDM) passive optical network (PON) which uses phase modulation (PM) of the optical carriers in the optical line terminal (OLT) in order to achieve inherent noise immunity in the network. In the demodulation of the optical PM signal at the optical network unit (ONU), we have proposed to use a simple injection–locked Fabry–Perot (FP) laser diode (LD) for achieving PM to intensity modulation (IM) converter which is followed by a photodiode to recover the specific channel information. A detailed analysis of PM–IM conversion in an injection–locked FPLD has been carried out and the viability of the proposed scheme has been established. The proposed UDWDM–PON which is a broadband access network is cost-effective and long reach.

Demonstration of Fully Softwarized 10G-EPON PHY Processing on a General-Purpose Server for Flexible Access Systems

Network requirements continue to expand, and flexible network deployment by utilizing software defined networks (SDNs) and network function virtualization (NFV) technology is a crucial subject. In order to maximize the advantages of NFV/SDN, we aim at expanding the software-defined region of optical line terminals (OLTs) by focusing on physical-layer (PHY) functions for the flexible access system architecture (FASA). While conventional studies limit the range of the softwarized region to upper layer processes, this article softwarizes both upstream and downstream PHY functions on a general-purpose server in real time, and, for the first time, introduces measured performance attributes including delay and throughput. We built a 10G service network interface (SNI) using multi-threaded processing and realized high multi-stream processing by using multiple-dimension buffers. The results gained from our demonstration system confirm throughput of 8.7 Gbps, which is the theoretical limit of 10G-EPON, and while satisfying the theoretical performance of FEC.